org.apache.flink.util.LongValueSequenceIterator Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.flink.util;
import org.apache.flink.annotation.Public;
import org.apache.flink.types.LongValue;
import java.util.NoSuchElementException;
/**
* The {@code LongValueSequenceIterator} is an iterator that returns a sequence of numbers (as
* {@code LongValue})s. The iterator is splittable (as defined by {@link SplittableIterator}, i.e.,
* it can be divided into multiple iterators that each return a subsequence of the number sequence.
*/
@Public
public class LongValueSequenceIterator extends SplittableIterator {
private static final long serialVersionUID = 1L;
/** The last number returned by the iterator. */
private final long to;
/** The next number to be returned. */
private long current;
/** The next value to be returned. */
private LongValue currentValue = new LongValue();
/**
* Creates a new splittable iterator, returning the range [from, to]. Both boundaries of the
* interval are inclusive.
*
* @param from The first number returned by the iterator.
* @param to The last number returned by the iterator.
*/
public LongValueSequenceIterator(long from, long to) {
if (from > to) {
throw new IllegalArgumentException(
"The 'to' value must not be smaller than the 'from' value.");
}
this.current = from;
this.to = to;
}
/**
* Internal constructor to allow for empty iterators.
*
* @param from The first number returned by the iterator.
* @param to The last number returned by the iterator.
* @param unused A dummy parameter to disambiguate the constructor.
*/
private LongValueSequenceIterator(long from, long to, boolean unused) {
this.current = from;
this.to = to;
}
public long getCurrent() {
return this.current;
}
public long getTo() {
return this.to;
}
@Override
public boolean hasNext() {
return current <= to;
}
@Override
public LongValue next() {
if (current <= to) {
currentValue.setValue(current++);
return currentValue;
} else {
throw new NoSuchElementException();
}
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
@Override
public LongValueSequenceIterator[] split(int numPartitions) {
if (numPartitions < 1) {
throw new IllegalArgumentException("The number of partitions must be at least 1.");
}
if (numPartitions == 1) {
return new LongValueSequenceIterator[] {new LongValueSequenceIterator(current, to)};
}
// here, numPartitions >= 2 !!!
long elementsPerSplit;
if (to - current + 1 >= 0) {
elementsPerSplit = (to - current + 1) / numPartitions;
} else {
// long overflow of the range.
// we compute based on half the distance, to prevent the overflow.
// in most cases it holds that: current < 0 and to > 0, except for: to == 0 and current
// == Long.MIN_VALUE
// the later needs a special case
final long halfDiff; // must be positive
if (current == Long.MIN_VALUE) {
// this means to >= 0
halfDiff = (Long.MAX_VALUE / 2 + 1) + to / 2;
} else {
long posFrom = -current;
if (posFrom > to) {
halfDiff = to + ((posFrom - to) / 2);
} else {
halfDiff = posFrom + ((to - posFrom) / 2);
}
}
elementsPerSplit = halfDiff / numPartitions * 2;
}
if (elementsPerSplit < Long.MAX_VALUE) {
// figure out how many get one in addition
long numWithExtra = -(elementsPerSplit * numPartitions) + to - current + 1;
// based on rounding errors, we may have lost one)
if (numWithExtra > numPartitions) {
elementsPerSplit++;
numWithExtra -= numPartitions;
if (numWithExtra > numPartitions) {
throw new RuntimeException("Bug in splitting logic. To much rounding loss.");
}
}
LongValueSequenceIterator[] iters = new LongValueSequenceIterator[numPartitions];
long curr = current;
int i = 0;
for (; i < numWithExtra; i++) {
long next = curr + elementsPerSplit + 1;
iters[i] = new LongValueSequenceIterator(curr, next - 1);
curr = next;
}
for (; i < numPartitions; i++) {
long next = curr + elementsPerSplit;
iters[i] = new LongValueSequenceIterator(curr, next - 1, true);
curr = next;
}
return iters;
} else {
// this can only be the case when there are two partitions
if (numPartitions != 2) {
throw new RuntimeException("Bug in splitting logic.");
}
return new LongValueSequenceIterator[] {
new LongValueSequenceIterator(current, current + elementsPerSplit),
new LongValueSequenceIterator(current + elementsPerSplit, to)
};
}
}
@Override
public int getMaximumNumberOfSplits() {
if (to >= Integer.MAX_VALUE
|| current <= Integer.MIN_VALUE
|| to - current + 1 >= Integer.MAX_VALUE) {
return Integer.MAX_VALUE;
} else {
return (int) (to - current + 1);
}
}
}